Field of the Invention
This invention relates to the field of solid state optoelectronic devices, optoelectronic integrated circuits, thyristor based light emitters, and spatially switching light emitters or amplifiers. More particularly, the present invention relates to compact devices for high speed spatial switching, or beam steering, of internally generated or amplification and high speed spatial switching of externally injected light.
Recent history has demonstrated that simple but more capable and functional optoelectronic devices are leading the way to advances in the fields of communications, pharmaceutical, transportation, and environmental applications. Thus, there is a long-felt need for simplifying semiconductor production.
The present inventors have addressed the long-felt needs for simplifying semiconductor device production in the field of optical switching networks by providing a device with a semiconductor structure for spatially switching light in optical switching networks with the bottom electrode designed for horizontal current flow as current enters the bottom region and dopants for free carrier concentrations in base and emitter layers sufficiently close in value to allow gate control of the location of a light emitting channel to occur. The present invention provides a simplified, compact, reliable and high speed semiconductor device for spatial switching of light emitter in optical switching networks in which only one component functions as both a light emitter and a spatial switcher, with switching accomplished by changing the bias of just a single electrode. By using fewer parts, the simplified spatial switching light emitter of the present invention provides longer semiconductor device lifetimes while still advantageously using increased semiconductor capability and reduced production cost. Due to this simplified structure, this invention's spatially switching light semiconductor thyristor based structures provide significant cost and operational advantages, without suffering from the drawbacks, limitations and shortcomings of increased production cost in prior art devices.
The prior art optoelectronic devices fall into four categories, light emitting thyristors, beam steering light emitters, spatially switching amplifiers and external cavity lasers.
Prior art thyristor structures include the silicon-controlled rectifier (SCR's), the gate turn off (GTO) thyristor and the MOS controlled thyristor (MCT), however, they do not have the capability of emitting light in two different locations at different times. They also employ a bottom electrode covering the entire lower surface, while the present invention's structure only covers a portion of that surface. Additionally, none of the prior art thyristor structures allow moving the light emission region using a single electrode as the present invention does. Further, most prior art thyristor structures have an operational speed based on fixing the gate's current, while the thyristor structures of this invention change potential bias at the voltage, rather than the current, of the gate.
Prior art does include a spatially switching thyristor that requires changing the bias at two electrodes in a correlated manner to reduce the light emission in one location and increase it in another. See for example, V. Korobov et al., vol. 1 of Proceedings of the Optical Engineering Midwest Conference, page 374, 1995. Since only one electrode is used in switching in the devices of the present invention, the number of external contacts are reduced, the parasitic effects of the additional electrode and the external contacts are eliminated, making the design and packaging of this structure more compact than other structures. In accordance with the present invention, using fewer parts should reduce manufacturing, alignment and assembly costs.
Prior art beam steering light emitters include a number of complex structures that do not provide the advantages of simplified production costs. While multiple frequency emitting lasers also exist, they are also suffer from increased complexity and higher production costs.
Having one device function as a beam steering light emitter allows manufacturers to reduce costs by avoiding time-consuming and costly retooling operations to switch from processing one device to another. Also, because the steering or switching function in these devices comes about by changing the bias at only one gate electrode, the process of designing the circuit in which these devices will operate is simplified and fewer components will be needed there as well. Also, the production steps during manufacturing are compatible with current layer deposition equipment available at most fabrication plants.
Moreover, the devices of the present invention also provide other hitherto unavailable advantages. These advantages include larger spatial separation of emitted light for the same overall device size when compared to waveguide based spatial switches because spatial switching is due to moving the light emission region rather than bending the light beam, good gain is provided because the control circuit which changes the voltage on the gate electrode is required to operate at roughly one-tenth the light emission channel current. Other advantages are ease of integration with other semiconductor devices, single electrode control, a faster turn-off that depends on drift diffusion for carrier removal rather than recombination and faster laser switching on and off. Another additional advantage is the capability to use different external cavities surrounding a single active region of a semiconductor laser, so that by changing only a single bias, the operator can modulate either the emitted light's wavelength or the repetition rate in a pulsed laser. The laser embodiment also permits turning lasing on and off by moving the light emitting electron-hole plasma in and out of the regenerative feedback cavity where high gain occurs. The present invention also provides added advantages of selectively amplifying optical signals and the simplified structure of all embodiments makes them easier to fabricate and grow than prior art devices. Due to this invention's simplified structure, these and other advantages are provided without suffering from the drawbacks, limitations and shortcomings of more complex and expensive prior art semiconductor devices.
Additionally, since current spatial switching speeds are limited to the nanosecond range by carrier dynamics, which includes their lifetime, the present invention's use of drift and diffusion for carrier removal from the light emission region during switching, eliminates this problem. Therefore, the devices of the present invention will allow for fast switching of light through different paths in an optical switching network. Furthermore, the devices of the present invention are polarization insensitive to amplify, and spatially switch, injected light.
Potential applications and uses of the devices of the present invention include optical signal processors, optical computers, optical interconnection networks, optical switching networks, high-rate data routers, and lightweight agile beam-steering units. Further, the three terminal devices of the present invention can take three electrical signals and emit spatially switching light, allowing for the design of systems where this device would be a logical bridge between an optimized electronic system and either one of two optimized optical system.
Prior art light emitting thyristors devices and structures are described in the following publications:
R. Pereika et al., "Optoelectronic Switch with Low Holding Power," 26 Electronic Letters No. 5, pp. 280-2, Mar. 1990;
Claisse et al., "Electrical and Optical Switching Characteristics of the Single-Quantum-Well DOES Laser," 39 IEEE Transactions On Electron Devices No. 11, pp. 2523-7, Nov. 1992; and
Buchwald et al., "A Three Terminal InP/InGaAsP Optoelectronic Thyristor," 41 IEEE Transactions On Electron devices No. 4, pp. 620-2, Apr. 1994.
Prior art light emitting beam steering light emitters devices and structures are described in the following publications:
Y. Sun et al., "Beam Steerable Semiconductor Laser with Large Steering Range and Resolvable Spots," 30 Electronics Letters No. 24, pages 2034-35, Nov. 1994;
Y. Sun, et al., "Thermally Controlled Lateral Beam Shift and Beam Steering in Semiconductor Lasers," 7 IEEE Photonics Technology Letters, No. 1, pp, 26-28, Jan. 1995;
L. Fan et al., "Dynamic Beam Switching of Vertical-Cavity Surface-Emitting Lasers with Integrated Optical Beam Routers," 9 IEEE Photonics Technology Letters, No. 4, pp. 505-7, Apr. 1995; and
S. M. Jackson et al., "Optical Beamsteering Using Integrated Optical Modulators," 15 Journal of Lightwave Technology No. 12, pp. 2259-62, Dec. 1997.
Prior art external cavity laser devices and structures are described in the following publications:
A. V. Chelnokov et al., "Ultrashort Pulses in Diffraction-Limited Beam From Diode Laser Arrays With External Cavity," 29 Electronics Letters No. 10, pp. 881-2, May 1993; and
S. Bouchoule et al., "Highly Attenuating External cavity for Picosecond-Tunable Pulse Generation from Gain/Q-Switched Laser Diodes," 29 IEEE Journal of Quantum Electronics No. 6, pp. 1693-9, June 1993.
Prior art spatially switching amplifiers devices and structures are described in the following publications:
W. K. Burns et al., "Active Branching Waveguide Modulator," 23 Applied Physics Letters No. 12, pp. 790-2, Dec. 1976;
H. Sasaki et al., "Theoretical and Experimental Studies on Active Y-Junctions in Optical Waveguides," vol. QE-14 IEEE Journal of Quantum Electronics No. 11, pp. 883-92, Nov. 1978; and
P. Granestrand et al., "Integrated Optics 4.times.4 Switch matrix With digital Optical Switches," 26 Electronics letters No. 1, pp. 4-5, Jan. 1990.